1. Field of the Invention
The present invention relates generally to luminaires for airfield lighting. In particular, the present invention relates to in-pavement directional luminaires for runways and taxiways including centerline, touchdown zone, threshold/end, edge, stop bar and the like.
2. Discussion of the Related Art
Although many specific improvements have been implemented in in-pavement luminaire designs, these basic improvements remain unchanged in that they generally consist of using an incandescent bulb as a light source combined with conventional optics as a beam forming element.
A number of disadvantages related to this design include high maintenance costs, specifically relating to relamping due to low bulb life-time (500 to 1,000 hours) and the inability of conventional optics to efficiently provide complicated spatial luminous intensity distribution, which results in very low efficiency (percents) and high power consumption.
A new generation of lighting devices is based on sold state technology. In addition to other benefits, light emitting diodes (LEDs) have high efficiency in that they produce more light per watt and they have an extremely long life. Recent advances have taken place in the area of directional LED lamp construction.
One of the basic categories of LED lamp construction is the implementation of multiple LEDs in a cluster to combine luminous flex from multiple LEDs using primary optics integrated in the LED for directionality. LED manufacturers offer a wide choice of primary optics including from 120° to 5° directionality.
This configuration is typically implemented for relative low intensity devices, but for high intensity LEDs, this conventional design is not practical because of space limitations and the small size of the window in in-pavement luminaires. Additionally, it is well-known that clusters of LEDs typically have various thermal problems, thereby negatively impacting on the photometric parameters such as luminous flux and color change.
The other basic category of construction of LED luminaire design is based on the use of secondary optics—an external to the LED optical element for the concentration and the direction of light.
In contrast to conventional optics, non-imaging optical elements are very efficient, specifically for LEDs with wide angular divergence. While one design consideration may be to combine the cluster design with the non-imaging optic for an application that requires high intensity light, this combination unfortunately requires an individual optical element for each LED.
What is needed, therefore, to overcome these limitations found in conventional designs is the application of multiple high flux LEDs with termostabilization using a single non-imaging element as a secondary optic.